FIXATION

ISOTEC Arsenic Fixation (IAF) Process Overview

Although iron (both with and without peroxide) has been used for years to precipitate and fix arsenic, achieving effective distribution under in-situ conditions has proven to be the weak link for successful projects. Direct injection of iron salts is often vulnerable to premature iron loss via sorption to native soil matrix.

ISOTEC’s Innovative Arsenic Fixation (IAF) process utilizes a balanced formulation of reagents to enhance radial distribution of iron and provide a source of dissolved oxygen. The IAF process co-precipitates arsenic via formation of an iron-arsenic oxyhydroxide complex. The IAF process requires both the iron and arsenic to be present in groundwater in an oxidized state (Fe+3 and As+5), while simultaneously providing a source of dissolved oxygen to allow the formation of the oxyhydroxide complex. The unique nature of the IAF Process stems from the use of a chelated iron catalyst and dilute stabilized hydrogen peroxide. The combination of these two reagents in-situ allows for optimal fixation chemistry and physical distribution of reagents.

The use of chelating agents allows for the iron to be stable in the subsurface at neutral pH while the stabilized peroxide is introduced into the groundwater to serve as the oxygen source. The reactions that occur when both peroxide and iron co-exist for extended periods of time (hours) allow for the groundwater conditions to become slightly oxidizing with an abundance of available dissolved oxygen from the decomposition of the peroxide while the arsenic is concurrently oxidized from As+3 to As+5 and iron is oxidized from Fe+2 to Fe+3.

In addition, the use of chelating agents and stabilizers slows down the decomposition rate of hydrogen peroxide. A benefit of slowed decomposition includes sufficient time for the produced gases to expand and generate a significant radius of influence (ROI) through displacement. A slowed decomposition also allows the chelated iron and stabilized peroxide to distribute throughout the ROI and remain available for fixation chemistry.